Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-03-31
2003-06-24
Nguyen, Hoa T. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06583970
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-246165, filed Aug. 31, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a head device applied, for example, to the read head of a disk drive. More particularly, the invention relates to a magnetoresistive head device employing a giant magnetoresistive (GMR) device (sensor).
In recent years, disk drives, such as hard disk drives (HDD), have employed a magnetoresistive head (an MR head) as a read head for reading out data magnetically recorded in a disk (i.e., a recording medium). Nowadays, it has become mainstream to use an characteristics-improved GMR element (such as a spin-valve sensor) as the MR head.
Normally, an HDD comprises a magnetic head device wherein a read head made of a GMR element and a write head made of an interactive thin film head are mounted on the same slider.
FIG. 9
is a conceptual diagram of a conventional GMR element and shows how the GMR element formed on a wafer looks like when viewed from above. A GMR layer
1
, exhibiting a magnetoresistive effect, joins electrode films (conductors)
90
at the respective ends. The electrode films
90
serve to cause a current flow.
FIG. 10
shows a sense current (broken-line arrows
100
) which flows from one of the electrode films
90
to the other through the GMR layer
1
. The sense current produces a magnetic field
101
acting in the direction indicated by the solid-line arrows.
It should be noted that the electrode films
90
are very high at the joint
91
where they are in contact with the GMR film
1
(the height being regarded as the width if viewed in the Z direction indicated in FIG.
9
). Due to this structure, the direction in which the sense current flows varies at the joint
91
. As shown in
FIG. 10
, therefore, the sense current (
100
) flowing down in the left electrode film
90
begins to flow horizontally when it reaches the joint
91
that adjoins the GMR film
1
. Having passed through the GMR film
1
, the sense current enters the opposing (right) electrode film
90
, where it changes in direction and flows again vertically.
Since the sense current changes in direction in this manner, the direction in which the generated magnetic field acts differs between the central part of the GMR film
1
and the end portions thereof (i.e., the portions in the neighborhood of the joints
91
), as indicated in FIG.
11
.
In the conventional GMR head, the electrode films
90
, with which the sense current is made to flow in the GMR layer
1
, have a greater height the height being regarded as the width if viewed in the Z direction indicated in
FIG. 1
than that the GMR layer
1
has at the joints, as described above. Due to this structure, the direction in which the sense current flows changes markedly in the neighborhood of the joints. As a result, the direction in which a free layer (i.e., an MR active region used for a reproducing magnetic field) included in the GMR layer
1
is magnetized differs, depending upon the portions of the GMR layer. The magnetization differs between the central portion of the GMR layer and the end portions thereof (the portions in the neighborhood of the joints).
This gives rise to the following problems.
FIGS. 12A
to
12
C show how the position of the read head of a HDD is related to a data track
120
(the track width of which is TW) of a disk (recording medium) when data (servo data or user data) are read out from the data track by the GMR element
1
of the read head. As shown in
FIG. 12B
, when the read head (GMR element
1
) is located within the range of the data track
120
, the amplitudes of positive and negative pulses of the signals read by the read head are substantially equivalent or symmetric (see FIG.
13
B).
As shown in
FIGS. 12A and 12C
, when the read head is shifted from the data track in the widthwise direction of the track (this state will be hereinafter referred to an “offtrack” state, the amplitudes of the positive and negative pulses of the read signals are asymmetrical. (See
FIGS. 13A and 13C
.) This phenomenon is attributed to the above-described magnetization direction of the free layer
1
included in the GMR layer
1
. That is, the direction in which the free layer is magnetized differs between the central portion of the GMR layer and the end portions thereof (see FIG.
11
). If the distribution of the magnetic layer of the GMR layer
1
is in this state, the magnetization is discontinuous in the magnetic domain structure of the free layer. This is considered to cause so-called Barkhausen noise.
Where the amplitudes of the positive and negative pulses of the read signal vary depending upon the position of the read head, as shown in
FIGS. 13A and 13C
, the servo data, with which the positioning of the head is controlled, may not be reproduced with high accuracy. Since this increases the positional shift of the head, the data reproduction operation, i.e., the operation for reproducing recorded signals from the disk, may not be performed with high accuracy. This problem is very serious if the data track width of a disk is decreased for high-density recording.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to enable an MR layer to be magnetized uniformly when a sense current flows. When the MR layer having this characteristic is incorporated in the read head, the amplitudes of the positive and negative pulses of a read signal do not become asymmetric, and the generation of Barkhausen noise is suppressed.
To attain this object, the present invention provides a magnetoresistive head device comprising: a magnetoresistive layer which exhibits different resistances in accordance with a magnetization direction corresponding to a magnetic field applied from a magnetic recording medium and a current flow direction of a sense current; and electrode sections (conductors) sandwiching the magnetoresistive layer in contact therewith and causing the sense current to flow. The electrode sections has joint portions which are in contact with the magnetoresistive layer, and these joint portions have substantially the same height as that of the magnetoresistive layer when measured from the surface of the magnetic recording medium (disk). The magnetoresistive layer is specifically a giant magnetoresistive (GMR) element (sensor) and includes a free layer. The free layer is an MR active region for detecting the recording magnetic field on the disk.
With this structure, the present invention enables the magnetization direction associated with a sense current to be as uniform as possible throughout the length of the free layer of the GMR layer, i.e., from the end portions in contact with the electrode sections to the central portion. Hence, when the MR head of the present invention is employed as the read head of a disk drive, stable read signals can be reproduced from the read head. More specifically, even when the read head is away from the target data track of a disk and is therefore in the offtrack state, the amplitudes of the positive and negative pulses of the read signal from the head can be controlled to be constant. In addition, it is possible to suppress the Barkhausen noise, which is due to the generation of a magnetic domain in the GMR layer. Owing to this feature, the read head can reproduce servo data, required for the positioning control of the head, from the disk with high accuracy. Consequently, the read error rate can be improved when data are read from the disk.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
REFERENCES:
patent: 5371643 (1994-12-01), Yuito et al.
patent: 5442507 (
Kabushiki Kaisha Toshiba
Nguyen Dzung C.
Nguyen Hoa T.
Pillsbury & Winthrop LLP
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